About 20 years ago, I worked for Walmart Optical Lab, where eyeglass lenses were

Question

About 20 years ago, I worked for Walmart Optical Lab, where eyeglass lenses were manufactured. There are several steps in the process of making these lenses. The department that I worked for made mostly transition and bifocal lenses. Each shift the percentage of defects or breakage was tracked for quality control. This control chart was continually updated and displayed for all employees to see. Management constantly reviewed these charts in order to determine if they represented common cause variation (which would indicate a stable system) or if they represented special cause variation (which would indicate that the system is out of control) (Statistical Control Charts, n.d.). Some of the common cause variables that may cause defects or breakage were: poor lighting, measurement errors, operator errors and equipment wear and tear. A special cause variable that may have stood out on the control chart in the optical lab would have been an incorrectly calibrated machine, as this would cut the wrong curve into almost every eyeglass lens that went down that assembly line.

Questions:

Is the process in control or out of control? Would the process be in control if Western Electric rules are considered? Explain your reasoning?

Explanation / Answer

The process was not in control and hence was shwn out of control. The Western Electric rules considered that there must be good calibration of measuring instruments. There must be good quality of glasses used in the manufacturing of the spectacles.

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